1. Field of the Invention
The present invention relates to the art of boresighting parallel line of sight detectors in the ultraviolet, infrared and/or visible wavelength bands with laser generated beams of radiation outside the detected bands.
2. Description of the Prior Art
Visible wavelength band TV detector systems are commonly employed aboard aircraft to sense images of the terrain or other targets within the field of view and to present those images to the pilot and/or others via a CRT display. In some instances, such as that discussed in commonly assigned U.S. Pat. No. 3,752,587, and incorporated herein by reference, a laser is also employed to direct an invisible beam of radiation onto a distant target that is in the line of sight of the visible band detector. It is, of course, most desirable to have the central line of sight of the visible band detector at the approximate center of the display screen reticle and to likewise have the line of sight aligned with the projection path of the invisible laser beam radiation.
In the case of the above referenced U.S. Pat. No. 3,752,587, a laser beam is projected and visible band images are received for detection via a common optical system along a common optical path. When it is desirable to boresight the reticle center on the display screen, a reflector element is rotated into the common path and diverts a portion of the projected laser beam to a lens. That lens focuses the beam onto an opaque surface, which is capable of being perforated by the invisible focused laser beam. The opaque surface is backlit with a source of visible band radiation and the perforation is imaged as a bright spot by a vidicon detector via the focusing lens and the reflector element. Boresight alignment can then be achieved by adjusting the reticle on the TV display so that its center coincides with the bright spot visible on the display, since the bright spot corresponds to the location of the laser beam projection path with respect to the displayed image.
The prior art method illustrates the use of an auxiliary light source and an advancing mechanism to supply an opaque surface for perforation by the focused laser. Each of these active elements increases the chance of failure, and requires an electrical supply.